/*
 * Copyright (C) 2012 Google Inc.
 * 
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not
 * use this file except in compliance with the License. You may obtain a copy of
 * the License at
 * 
 * http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
 * License for the specific language governing permissions and limitations under
 * the License.
 */

package interactivespaces.event.trigger;


/**
 * A trigger which can be observed.
 *
 * @author Keith M. Hughes
 */
public interface Trigger {

	/**
	 * Get the current state of the trigger.
	 * 
	 * @return
	 */
	TriggerState getState();

	/**
	 * Add a new listener to the trigger.
	 * 
	 * @param listener
	 * 		The new listener to add.
	 */
	void addListener(TriggerListener listener);

	/**
	 * Remove a listener from the trigger.
	 * 
	 * <p>
	 * Does nothing if the listener wasn't registered with the trigger.
	 * 
	 * @param listener
	 * 		The listener to remove.
	 */
	void removeListener(TriggerListener listener);
}
